Trace Metal and Nutrient Biogeochemistry

GEOTRACES is an international research program dedicated to understanding the biogeochemical cycling of trace elements and their isotopes in the global ocean. The GP17-OCE and GP17-ANT cruise tracks, shown in Figure, surveyed and collected samples from the South Pacific and Southern Oceans. This study investigates the composition of trace element-binding ligands and their role in ocean biogeochemistry across contrasting regimes, known as low-productivity High Nutrient Low Chlorophyll (HNLC) regions and high biological productivity areas. Using advanced analytical techniques, including liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) and inductively coupled plasma mass spectrometry (LC-ICPMS), we aim to characterize the chemical identity of natural ligands and siderophore biomarkers. This unique dataset will be integrated with nutrient and biological productivity measurements to provide deeper insight into trace metal cycling and marine biogeochemical processes.

Despite accounting for approximately 5% of Earth’s land mass, wetland ecosystems store a staggering 20-30% of global terrestrial carbon. This makes wetlands a critical ecosystem for the carbon cycle. Our goal is to elucidate the biogeochemical cycles controlling carbon sequestration and flux from wetland systems. We do this by utilizing mass spectrometry techniques coupled to liquid chromatography to study how organic carbon changes forms across important mechanisms such as colloid formation and changes in redox conditions. Our findings give insights for large data models that predict the potential for wetland systems to act as carbon sinks or emission sources in the face of changing environmental conditions. 

Nitrogen (N) is a limiting element in most of the surface ocean. Particularly, the primary productivity of phytoplankton is limited by the availability of dissolved organic nitrogen (DON). DON is the nitrogen-containing component of dissolved organic matter derived from the biosynthesis and decomposition of plants, algae, and microbes. There are various sources of DON contributing to the total DON pool in the ocean, such as river, submarine groundwater discharge, and N2 fixer Trichodesmium. Different sources of DON have distinct composition, bioavailability, and persistence. To differentiate DON from different inputs and track their fate, we use ultrahigh performance liquid chromatography with tandem Orbitrap mass spectrometry to characterize molecules, combined with computational algorithms (CoreMS) for data processing and analysis.

Mineral-associated organic matter (MAOC) is an important terrestrial carbon sink, though its biological sources and mechanisms of formation are not fully understood. Lignin is a heterogeneous biopolymer that comprises up to 60% of plant woody tissue and is the largest terrestrial source of aromatic carbon. It is broken down in soils to small molecule products by soil bacteria and fungi, and these products strongly resemble MAOC in composition. This project aims to understand the processes behind MAOC formation by examining adsorption capacities of lignin degradation products to soil minerals. This is a collaborative project with the Penn group here at UMN.

The vast majority of iron in seawater is bound to organic ligands such as siderophores, strong iron-binding molecules synthesized by microbes to acquire iron, which control marine iron solubility, transport, and bioavailability. Photochemical processes can influence the iron binding properties and chemical identity of these organic ligands. Determining the extent to which natural light interacts with these ligands in the euphotic zone is important to understanding the fate of iron and other trace elements across the surface ocean. This study investigates the photodegradation of marine siderophores and sediment-derived organic matter, probing reaction kinetics, photolysis products, and the resulting chemical speciation of iron in surface waters. In addition, these studies aim to determine whether photochemistry generates halogenated organic matter, which is found at elevated concentrations in oligotrophic surface waters.

Biochar is an environmentally friendly material produced through high-temperature pyrolysis of organic matter and is commonly used for contaminant removal. However, the removal of trace-level contaminants such as perfluorooctanoic acid (PFOA) typically requires either prolonged treatment durations or large quantities of biochar. To enhance removal efficiency and reduce material requirements, this project aims to develop an engineered biochar suspension (as shown in the Figure) with amphiphilic properties, consisting of deflocculated, nano-sized particles with optimized surface area for extended removal capacity and faster kinetics. These advanced biochar formulations are being specifically tested for PFOA removal using EPA-approved LC-MS/MS method for testing.

The Southern Ocean has high nitrogen levels and low iron levels. With relatively low access to iron, phytoplankton growth and productivity is limited. In the developed curriculum, students explore the phenomenon of iron limitation by culturing Chlorella vulgaris in a control F/2 nutrient solution and an experimental modified F/2 nutrient solution containing no iron. Students make quantitative measurements by taking population samples from each algae solution to determine how iron limitation affects population growth as well as collecting dissolved oxygen data to compare gross primary productivity. Ultimately, students use these methods to determine the potential implications of iron fertilization in the ocean and whether it is a viable solution to climate change.